A well system (e.g., an oil or gas well) can include a wellbore drilled into a subterranean formation. These wells may have oil, water, and gas fluids. These fluids may be in multi-phase mixtures, such as mixtures of water, gaseous hydrocarbons, and fluidic hydrocarbons. Each phase may have a different density, viscosity, compressibility, elasticity, and acoustic impedance. In order to evaluate the commercial value of such a hydrocarbon producing well, it can be useful to analyze the thermophysical properties of the formation fluid in-situ.
Different physical sensors (e.g., a capacitance sensor, sonic sensor, or resistivity sensor) or chemical analytical sensing instruments (e.g., an optical fluid analyzer) can be packaged into a downhole tool for analyzing well fluid. One example of a downhole tool for analyzing well fluid can be a reservoir description tool (RDT). The RDT can include sensors for analyzing various physical and chemical properties of the downhole fluid. The sensors can include a densitometer for determining the density of the fluid.